Construction of a Multiway Carbon Nanotubes Loudspeaker with Finely Tunable Resonance Frequencies

Abstract

The sound pressure generated by thermo-acoustic (TA) loudspeakers is proportional to the frequency of the sound. This characteristic yields a low sound pressure level (SPL) in the low-frequency region, hindering the practical application of TA loudspeakers. The limitation of low SPL is approached by using a resonating structure, in which a TA sound generator, such as multiwalled carbon nanotube sheet, is enclosed within a cavity covered by a vibrating plate. However, the cavity-plate resonator produces an amplified SPL only around the resonating frequency, so its operating frequency bandwidth is narrow. Hence, a multiway TA loudspeaker consisting of multiple resonators that can amplify sound over a wide frequency range is designed. An accurate mechanical model is presented for predicting the resonance frequency and it shows that the behavior of resonators designed from the proposed model matches the theory well. The model enables the fine-tuning of resonances through the application of different materials for a resonator plate and by changing the structural dimensions. A crossover network for combining multiple TA resonators is designed, and the total frequency response shows a flat frequency response with amplified SPL. These improvements open up possibilities for the use of TA loudspeakers as a practical audio device.